Subterranean piping systems of the type that are typically installed at service stations are generally utilized to communicate fuel or chemicals between an underground storage tank and an above ground dispensing station. The underground storage tanks and associated piping pose serious potential environmental and fire hazards as the chemicals contained therein could and have in the past leaked into the earth.
Oil companies have been under considerable pressure to ensure that environmental concerns are given priority in the planning and installation of petrol station infrastructures. This has not been without significant on-cost. One important advancement has been the use of pipeline systems constructed from plastics materials which have enabled the oil companies to install cost-effective environmentally acceptable alternatives to steel pipework systems which tend to corrode over time.
Moreover, over recent years there have been major developments in fuel technology which have culminated in commercially available alternative fuels containing additives which have replaced lead-based antiknock compounds. Research also continues to centre on reducing sulphur content and hazardous emissions from fuel. In order to eliminate lead and sulphur from fuels, exotic additives and octane enhancers such as MTBE (methyl tertiary butyl ether) have been developed which are based on complex organic or heavy metal organic additives.
The presence of these additives in fuel can give rise to major environmental issues. Some such issues are described in an article entitled “MBTE—How should Europe Respond”, in Petroleum Review February 2000 pages 37-38. The entire text of this article is incorporated herein by reference by way of background information. The authors conclude that lead and some other metals are the most effective octane enhancers. However, lead is in the final stages of being phased out because of environmental and health issues, and the most readily available alternative, MMT (methylcyclopentadienyl manganese tricarbonile) is currently not widely accepted. The only other octane enhancers currently available are MTBE and other ethers such as ethyl tertiary butyl ether (ETBE) and tertiary amyl methyl ether (TAME), or alcohols such as ethanol. The ethers all tend to have similar properties and drawbacks. Ethanol is already used as a gasoline-blending component in parts of the United States where it is readily available, and in Brazil. It is an effective octane booster but has a number of drawbacks: it needs a “water-free” distribution system and is not without ground water issues. It is currently not recommended by the motor industry and is not cost-competitive.
The introduction of new fuel mixtures and esoteric additives has led oil companies to question whether existing pipeline systems can cope with the new fuels with regards to mechanical performance and permeability resistance. In some instances this will result in the pipework having to be replaced by pipework made from a more resistant material, with all the disruption that entails.
In petroleum forecourt installations, pipework running between dispensing pumps and a subterranean fuel storage tank passes into a manhole chamber which is situated directly above the manhole lid of the tank. The chamber is normally defined by an upstanding wall which, when viewed from above, can be of an octagonal, square, circular or rectangular shape, and which includes apertures through which respective pipes pass.
To overcome environmental concerns this pipework is now generally constructed from plastics materials and many current designs of forecourt installation utilise secondary containment. This involves containing each fuel supply pipeline in a respective secondary containment pipeline which is optionally sealed at its ends to the fuel supply pipeline. The secondary containment pipeline prevents leaks from the fuel supply pipeline from being discharged into the environment, and also can convey leaked petrol to a remote-sensing device. Typically, the pipes forming the secondary containment pipeline are initially separate from the fuel pipes and are sleeved over the latter as the fuel pipes are installed between the fuel storage tanks and dispensing pumps.
A common material for the chamber to be constructed from is glass-reinforced plastic or, more generally fibre-reinforced plastic (FRP), which involves moulding a resin or other polymeric material reinforced with fibres such as glass fibres.
It is desirable to provide a seal between each of the apertures and its respective pipe to avoid ingress of water into the manhole chamber. To that end, it is known to attach a fitting to a portion of the wall around the aperture and a rubber “boot” that sleeves over the pipe and is clamped to both the pipe and the fitting by, for example, Jubilee™ clips. Some types of such fitting are bolted to the chamber wall, whilst other types of fitting provide inner and outer parts between which the wall is sandwiched, the inner and outer parts being held together by a screw-threaded connector which extends through the aperture. These connectors often incorporate a rubber seal located between a part of the connector and the chamber wall.
Neither type of fitting provides a completely effective seal.
Over time, both types of seal can allow water to leak into the manhole chamber and to accumulate in a pool in the bottom of the chamber. This in turn makes the maintenance of the chamber bottom and tank entrance extremely difficult. In addition a defective seal can allow any petroleum fluid or vapours which find their way into the chamber to escape into the environment.
It would be preferable if such a fitting could be chemically bonded or electrofusion welded both to the pipe and to the chamber wall. One type of such fittings, manufactured from a plastics material capable of electrofusion to both the pipe and the chamber wall is known from GB2332255 (PetroTechnik Ltd). However, these fittings cannot be used when the chamber is constructed from GRP, a material commonly used in construction of chambers and sumps for this application.
In summary therefore, in the event that pipework has to be replaced, or in new build situations, there is a requirement to seal pipework made from polyethylene, polypropylene, polyamide or the like to a GRP chamber wall. Accordingly it is an object of the present invention to provide a fitting for forming a seal between pipework formed from a plastics materials and a GRP chamber which overcomes some or all of the above disadvantages.